1. Field of the Invention
The invention relates to a method of transmitting a digital video signal via a transmission medium, comprising a transmitter for transmitting and a receiver for receiving the digital video signal, in the transmitter:
each picture of consecutive pictures of N.times.M picture elements being sub-divided into sub-pictures, a sub-picture being assembled from n.times.m picture elements, it holding for the product of n and m that it is greater than or equal to 4, PA1 for a sub-picture and for a video signal component associated with each one of the picture elements in the sub-picture, the maximum value and the minimum value this video signal component has in the sub-picture being determined with the object of obtaining the dynamic range of the video signal component for the picture elements in the sub-picture, PA1 the amplitudes of the video signal component in the sub-picture all being quantized by a given number of p bits by subdividing the dynamic range into 2.sup.p of at least approximately equal sub-ranges, PA1 the quantized amplitudes of the video signal component for all the picture elements in the sub-picture and information about the minimum value and the maximum value of the video signal component in the sub-picture being applied to the transmission medium for transmission via the transmission medium, PA1 the information about the maximum and minimum values of the video signal component in the sub-picture, and the quantized amplitudes of the video signal component for all the picture elements in the sub-picture being received, PA1 the quantized amplitudes of the video signal component in the sub-picture being dequantized, PA1 the video information for consecutive pictures of N.times.M picture elements being derived for consecutive pictures,
in the receiver:
and a receiver for use in the method.
2. Description of the Related Art
The method of the type defined in the opening paragraph is disclosed in the U.S. Pat. No. 4,729,021. More specifically, FIG. 8 of said Patent shows how the method is performed. The video signal component to be encoded can, for example, be the luminance component or a chrominance component of the video signal. In a sub-picture, the maximum value (U.sub.max) and the minimum value (U.sub.min) of the video signal is determined. The difference between these two values then indicates the dynamic range (DR) of the video signal component in the sub-picture. The minimum value of the video signal component in the sub-picture can thereafter be subtracted from the amplitude of the video signal component associated with the picture elements in the sub-picture. The amplitudes A thus obtained are located in a range for which it holds that 0.ltoreq.A.ltoreq.DR. The amplitudes thus obtained are now quantized. If it has been ascertained that the amplitudes in the video signal component in the sub-picture are quantized by p bits, then the dynamic range is subdivided into 2.sup.p equal sub-ranges (DB). Let p be equal to 2, then the dynamic range is divided into four equal sub-ranges. Amplitudes in the sub-range between 0 and 1/4 DR are then represented by the binary number 00, amplitudes in the sub-range between 1/4 DR and 1/2 DR by the binary number 01, amplitudes in the sub-range between 1/2 DR and 3/4 DR by the binary number 10 and amplitudes in the sub-range between 3/4 DR and DR are represented by the binary number 11.
Dequantization at the receiver end means that the binary number 00 is converted into an amplitude 1/8 DR, the binary number 01 is converted into an amplitude 3/8 DR, the binary number 10 is converted into an amplitude 5/8 DR and the binary number 11 is converted into an amplitude 7/8 DR. By thereafter adding the value U.sub.min to the dequantized values, the dequantized amplitudes for the decoded video signal component for the picture elements in the sub-picture are obtained.